Lead-antimony alloy electroplating bath



Patented Apr. 7, 1953 JAaron LJHitchensfNew Hayen,(3onn.,-ani1ZR6bert Owens, Woo'd jRiver, "-'Ill,, assignors to 01m Industries, 1110., East Alton, 3111., :a corporation Noinrawing. Applicatinnflullflll#1316. .iSeitial No. 761813.68

iBi'GlalimS.

"This finvention relates fto *the .eiectr ep i i :oiimtalsan'd' more p articularlyfto. the gelectrodep- 'osition .or .lrlead-ariti ony alloys *from qu us ssilutions.

.fIhe .leotro'deposition .ofileadeantimony alloys "from aqueous solutions of certain .Ojf the metal salts .has .-.been described iheretofore. For Zin- .,s'.tanc e, .itlhaslbeen proposed .to plateilead-jantimom. alloy jfrom a ,iiuoborate ,or fluos'i1icatep1atingloath .(TheTMetaliIndustry, vol.1'1'8,'fNo. firp'e es .264 110.266, 1920) .and ifrom 1a tartraite bath con- ;taininaphenol sulphonic acid (KorroziyatiBorba sNi 6:"13032, pages "48to 14919142. ),,Ibutthe.1ead- .antimonycoatingsobtainedihy such methods'have "beenioundtobeiniierior tothe usuaimetal coat- ,ings such as .zinc fin preventing the corrosion of steel.and.similarmetal'bases.

.It is therefore anrobject of this invention to provide means for'forming alead-antimonyalloy coating havingimproved protective characterj-listics.

Another object of the invention is to provide anew plating bath .ior the electrodeposition of "lea'd-antimonyalloy.

.gstillanother object of theinvention is to providemeansfor improving thecorrosionres'istance of steel andQthermetaIs.

These and ,other objects and advantages are obtained inaccordance withthis invention byfthe provision .of a.novel platin g bath .in which the cations, lead .and antimony, are associated with a combination .of tartrate and .fiuoborate anions. .It;has. now- .been found that a lead-antimony alloy .coating can be electrodeposited from such a bath .with protective characteristics -greatly improved --.over those of ajlead-antimony alloy coatin electrodepositefd from a .bath containing .only tartrate :oronly fluoborateanions. For instance, smooth, uniform, adherent lead-antimony alloy coatings substantially free of pin holes and the like may abe .electrodepositedon steel in accordance with this invention .to provide steel-base articles .having a corrosion resistance and othercharacter- .istics greatly superior to similar steelarticle's providedwiththe usual platings of zinc,-.or copper or .thelike. I

Theelectroplatingbath of this invention em- ;.ployed ,in .accordance with well-known plating practice. For instance, as is customary in the .plating. of .lead from ;fiuoborate solution, the bath and free ;.boric acid, :or their equivalent, and a tsuitable-additionzagent,such :as glue, the fluoboric ibeing wp esent .to "increase .the :conductivity :wstabihzer to preventide'compositmn of -thei fluoq bora'te'and the glue or totheradditionagentbeing present'fto "control among -other things ithe -grain :size in the 'electrodeposite'd -film. The -efiect o'f "andznecessity :for the 'use of such "agents or'ad- .dition agents "inan .electroplating "bath garewellknown inthe'art.

The electroplating bathm'f this invention *may Lbe "employedffor"electrodepositing leadeantimony "alloys of practically "any desired composition, ifor instance the antimony content "may 'frange from ,merely a trace inthe coatmguptmamointwhere fithe alloy consists "Qf a preponderance of anti "mony. Various means, well known in "the art or ,plating alloys, may be employed to regulate "the composition .of the electrodeposited alloy. *For instance, the .ratio of lead *to antimony :'in "the plating is affectedto a certain extent'by changes ,in temperature and current density .during the electrodeposition. "Similarly the composition of the alloy plate may be vregulated by. the :compo sition of the platingbath, that is, it'maybe stated Lin general thatthe, percentage ofantimonyinith'e plate increases with anincreased content of'antimony intheplating bath. 'For this reason, the antimony content ,of the plating bath ,should'be regulated such as .to give the desired antimony content in "the electrodeposited "film.

The plating bath may'be preparedjin any suit- ;able manner. .In one preferred method, how- .ever, metallic antimony isdissolved in .a mixture ofnitricand hydrofluoric acids. Tartaricacid .is then added to the solutionand the mixture is .heated .until the .reddishfbrownefrumes of oxides of nitrogen are .no longer given off. his important that substantially all .thenitrate'be removed in this operation ,since the presence vo'f nitrate ion tends to cause the deposition of an uneven plate. The solution is then .cooled and mixed withanaqueous solutionof lead fluoborate containing free .fluoboric and .boric acids. The preparation of the bath ,is then completed Thy adding an addition agentsuch ,as glue.

Other oxidizing agents, .for example hydrogen peroxide, may be used in place .of the .nitric :acid in dissolving metallic antimony .for addition :50 should containragents'such as .free fluoboric acid :of ith'B- SOIUHOII, the :boric .acid :being present as to the plating bath, although -.nitric acid ,is .preferred :and good results can be obtained if the .antimonyiszaddedto vthezbathin the form of anti- :mony fluoride, antimonytartrate, or potassium :antimonyl tartrate.

in order to furthergclarify theinventionfollowing is a .detail description .;of the preparation and application of a plating .bath: illustrating 'iembodimentofithexinvention.-

A plating bath suitable for the electrodeposition of a lead-antimony alloy containing about 8% to 10% antimony is prepared by first dissolving about 200 grams, 1. e. about 200 parts by weight, of antimony in about 500 cubic centimeters, iwe. about 650 parts by weight of an aqueous solution containing 24% of hydrofluoric acid, i. e. 150 parts by weight, and 35% of nitric acid 1. e. about 230 parts by weight. About 400 grams oftartaric acid, 1. e. about 400 parts by weight, in about 200 cubic centimeters or parts by weight of water are then added and the mixture is heated until the reddish-brown fumes of oxides of nitrogen are no longer given ofi and the solution is then cooled.

About 4882 cubic centimeters, or about 6800 parts by weight, of an aqueous solution acidified with about 5% boric acid and containing about 660 grams per liter of lead fiuoborate and 35 grams per liter of free fiuoboric acid is diluted .with water to a total volume of about 22.7 liters, ;i. e. to a total of about 24,600 parts by weight, and

the diluted solution and the solution of antimony prepared as described above are then mixed.

.The resulting mixture thus contains about 200 parts by weight antimony, about 340 parts by weight boric acid, about 3200 parts by weight lead fiuoborate, about 400 parts by weight tartaric acid, and about 170 parts by weight fiuo- --boric acid, or stated in terms of anions and cations, the mixture contains about 200 parts by after the usual electrolytic and other cleaning .operations, are treated in a solution containing 'one mol of zinc chloride and one mol of ammonium chloride per liter of water at room temperature for about five minutes. The heads are then washed and placed in the electroplating bath prepared as described above.

The electroplating is carried out in the usual type of plating barrel. Lead anodes, or anodes of lead-antimony alloy containing about 8% antimony, are employed with a current density of about amperes per square foot for a period of about minutes at a temperature of about 80 to 85 Fahrenheit. By coating the shot-shell heads under such conditions, a coating of an alloy of lead containing about 8% to 10% antimony is obtained, about 0.00025'inch to 0.0005 inch thick. Immediately after the plating process is finished .the shot-shell heads are washed and then dried and polished, preferably by tumbling in any suitable vessel with clean sawdust.

When such shot shell heads have gone through the assemblying operation necessary to form a loaded round of ammunition and are subjected to a spray of 20% sodium chloride solution at a temperature of 95 F., in accordance with the standard A. S. T. M. Salt Spray Test Specification No. B-11'7 -41T, it is found that the heads will remain in the spray for as long as from 6 to 24 and more hours without corroding. In comparison, steel shot shell heads coated with copper or zinc about 0.0005 inch thick, after the as- ,semblying operation show signs. of "corrosion .4 products after only about 1.5 to 6 hours in the salt spray.

Although the plating of steel is described in the above specific embodiment it should be understood that the plating bath of this invention may be employed to electrodeposit lead-antimony alloys on other ferrous metals and non-ferrous metals, for instance copper or brass.

Although, as described above, the plating bath of this invention contains free fluoboric acid and boric acid, or their equivalent, and an addition agent such as glue, and may contain antimony fiuoride and the like, the essential and identifying characteristics of the bath are that it contains lead and antimony cations associated with broth tartrate and fiuoborate anions. The exact association, structure and inter-relation of the cations and anions of the bath are unknown and likewise the theory of operation of the bath is not completely understood. It has been found, however, that if the bath contains lead, antimony, fiuoborate and tartrate and the practice, well known in the electroplating art, of adding other suitable agents and addition agents to the bath is followed, an electrodeposited film of lead-antimony alloy may be obtained superior to that obtained from either a tartrate or a fiuoborate bath.

This invention accordingly provides a novel electroplating bath suitable for electrodepositing a film of lead-antimony alloy having improved proving the corrosion resistance of steel and other metals, and thus opens a wide field for the application of such alloys.

It is to be understood that the embodiments of the invention described herein are only illustrative and that many changes may be made therein without departing from the spirit and scope of the invention as set forth in the following claims.

Having thus described the invention, what is claimed and desired to secure by Letters Patent is:

1. The process of making an electroplating bath suitable for the electrodeposition of leadantimony alloy, which comprises dissolving antimony in a mixture of concentrated nitric and hydrofluoric acids, adding tartaric acid, heating said solution until the oxides of nitrogen are no longer given off, and thereafter mixing said solution of antimony with a lead fiuoborate plating bath composed of an aqueous solution of lead fiuoborate, fiuoboric acid, and boric acid.

f'ing ingredients in the proportion of about 340 parts by weight 'boric acid, about 3200 parts by weight lead fiuoborate, and about 170 parts by weight fiuoboric acid, and adding thereto about 50 parts by weight animal glue dispersed in hot water.

3. In a process for forming an electroplating bath for the electrodeposition of lead-antimony alloy, the steps of incorporating antimony into said bath which comprise dissolving about 200 parts by weight antimony in an aqueous mixture of about parts by weighthydrofiuoric'aoid and about 230 parts by weight nitric acid, adding about 400 parts by weight tartaric acid thereto and heating the solution until reddish-brown fumes of oxides of nitrogen are no longer given oil, and thereafter mixing the so-formed solution of antimony with a solution of lead fluoborate containing free boric acid and free fluobcric acid. 7

4. A bath suitable for the electrodeposition of a lead alloy containing about 8 to 10% antimony having as its functioning ingredients in an aqueous medium antimony, lead, fiuoborate anions, and tartrate anions, said ingredients being substantially in the relative proportions of about 200 parts by weight antimony cations, about 1700 parts by weight lead cations, about 1600 parts by weight fluoborate anions, and about 300 parts by weight tartrate anions.

5. In the process for forming an electroplating bath for the electrodeposition of lead-antimony alloy, the steps of incorporating antimony into said bath which comprise dissolving about 200 parts by weight antimony in about 650 parts by weight of an aqueous mixture containing about 150 parts by weight of hydrofluoric acid and about 230 parts by weight of nitric acid, adding about 400 parts by weight tartaric acid dispersed in 200 parts by weight water thereto and heating the solution until the reddishbrown fumes of oxides of nitrogen are no longer given off, forming a mixture of this solution with about 24,600 parts by weight of an aqueous solution containing about 340 parts by weight boric 6 acid, about 3200 parts by weight lead fluoborate,

and about 170 parts by weight fluoboric acid, and

adding thereto about parts by weight animal glue dispersed in about 700 parts by weight water.

AARON L. HITCHENS. ROBERT G. OWENS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 792,307 Betts June 13, 1905 952,704 Boessneck Mar. 22, 1910 1,780,944 Roscher Nov. 11, 1930 FOREIGN PATENTS Number Country Date 629,071 Germany Apr. 22, 1936 130,302 Great Britain July 29, 1919 OTHER. REFERENCES Knox, Metal Industry, vol. 18, No. 6 (June 1920), pp. 264-266. V

Mellor, Treatise on Inorganic and Theoretical Chemistry, vol. IX, (1929) pp. 381, 463.

Korroziya i Borba s Nei 6, N0. 2, (1942), DD. 48-49.

Chemical Abstracts, vol. 37 (1943), p. 1336.

Transactions American Electrochemical Society, vol. 28 (1915) pp. 325-338. 

4. A BATH SUITABLE FOR THE ELECTRODEPOSITION OF A LEAD ALLOY CONTAINING ABOUT 8 TO 10% ANTIMONY HAVING AS ITS FUNCTIONING INGREDIENTS IN AN AQUEOUS MEDIUM ANTIMONY, LEAD, FLUOBORATE ANIONS, AND TARTRATE ANIONS, SAID INGREDIENTS BEING SUBSTANTIALLY IN THE RELATIVE PROPORTIONS OF ABOUT 200 PARTS BY WEIGHT ANTIMONY CATIONS, ABOUT 1700 PARTS BY WEIGHT LEAD CATIONS, ABOUT 1600 PARTS BY WEIGHT FLUOBORATE ANIONS, AND ABOUT 300 PARTS BY WEIGHT TARTRATE ANIONS. 